It is sometimes desirable, during surgery, for a user to place a marking/guide pin, guiding wire, or other elongate marker (hereafter referenced as a “guidewire”) into penetrating engagement with a patient tissue. This “landmarking” via a guidewire may be helpful, for example, during orthopedic surgery. One example of a suitable guidewire is disclosed in co-pending U.S. Provisional Patent Application Ser. No. 61/362,722, filed Jul. 9, 2010, and titled “Method and Apparatus for Providing a Relative Location Indication During a Surgical Procedure”, the contents of which are hereby incorporated by reference in their entirety.
Once the guidewire has been placed in a desired location, and, optionally, at a desired trajectory, a cannulated tool (e.g., a drill), implant (e.g., a bone screw, acetabular component, glenoid component, bone plate, or the like), and/or other component (hereafter, “device”) may be passed over the guidewire and guided into contact with the patient tissue as desired. One skilled in the art will readily appreciate that a cannulated device refers to a device having a small diameter through-passage throughout at least a portion of the entire length of the device, optionally coaxial with the device, that can be configured to insert a guidewire therethrough.
One aspect of surgery in which a guidewire may be helpful is in guiding a cannulated drill into a patient tissue (e.g., a bone tissue) to create an aperture having a desired location and trajectory. However, the user often will also desire the aperture to have a particular depth (i.e., distance of insertion of the drill bit into the patient tissue). This measurement may be particularly important when the user is striving to avoid complete penetration and “punching through” the body tissue.
In the field, the insertion depth has been difficult to determine interoperatively from mere visual observation of a penetrating device, either in cannulated/wire-guided or “freehand” operation modes. Several prior art depth indicators have been proposed as aids to determine insertion depth of a device into a patient tissue. These depth indicators tend to be one of two styles: a simple probe inserted into the aperture in the patient tissue to directly measure depth, or a measuring structure attached to the device and contacting the patient tissue beside the aperture. Both of these styles have disadvantages. The former style requires removal of the device from the aperture before measuring can take place, and thus real-time measurement cannot occur. The latter style presumes that the nearby patient tissue is the same distance from the tool as the patient tissue being penetrated (which is not always the case) and also often is device-specific and not useful with a variety of devices. Another drawback to these two prior art device styles is that direct contact with the patient tissue is required, which could lead to patient tissue damage and/or contamination.